Typically, fiber optic cables installed in or between buildings to enable intra-organizational data and telephone communications are housed in conduits and connected with de-matable connectors. The benefits of fiber optics for use in these local networks are many; however, the primary benefit lies in the ability to send the information of many telecommunication instruments over an exceedingly small number of channels as compared to conventional copper cables. A single pair of optical fibers may, in fact, replace several hundred pairs of copper cables.
Because of the present tendency toward high capacity small cables, fiber optic cables are often installable where conventional copper or coaxial cables of equivalent capacity will not fit, e.g., small or congested cable ducts. Copper or coaxial cable bundles are large as 100 mm in diameter can be avoided in favor of fiber optic cables as small as 3 mm in diameter.
Unfortunately, single channel de-matable fiber optic connectors used to terminate the cable are typically 8 to 20 millimeters in diameter. This results in connector bundle sizes several times the diameter of the cable. For example, a typical AT&T Technologies connector used to terminate a typical 6 channel, 8 mm diameter, fiber optic cable will result in a bundle size of 36.7 mm which is over four (4) times the size of the cable. The National Electrical Code limits a single cable to 53% of the conduit area. Thus, the 8 mm cable can easily fit a 1/2 inch standard conduit. The same cable with pre-installed connectors would require a 11/2 inch standard conduit just to clear the connector bundle. Pulling equipment may dictate an even larger size conduit. The existence of previously installed cable and/or a series of 90 degree conduit bends might raise the required conduit size even higher. To compound these problems, the typical cable grip used to install cables in conduits does not expand more than a few percent larger than the minimum allowable cable diameter, i.e., it will not fit over a connector bundle with a diameter more than a few percent larger than the cable diameter.
This situation has almost universally resulted in field connectorization (as opposed to the more desirable factory connectorization) of duct-installed fiber optic cables. Unfortunately, to install the typically epoxy and polish connector takes approximately 20 to 40 minutes per end (two ends per connection) requiring approximately 40 separate steps. For example, some of these required steps include: (1) stripping the jacket away from the cable; (2) folding back the Kevlar material and stripping the buffer material; (3) cleaving or putting a break in the fiber such that the break is perpendicular to the axis of the fiber; (4) cementing the fiber inside of the connector with epoxy; and (5) polishing the fiber optic connector. The connectors may each cost as much as $25.00 or more. An incorrect installation or accidental breakage of the fragile fiber may necessitate that the connector be cut off, discarded and a new installation procedure begun having to again perform all of the time-consuming steps including that of polishing the connector which is perhaps the most time-consuming. As a result, field installation of de-matable connectors is performed by highly skilled personnel. It is not uncommon for this connectorization to be done by highly skilled, degreed engineers.
In a previous U.S. Pat. No. 4,711,517, the authors address the issue by providing for coupling nut installation after cable installation by pushing the coupling nut, which has an expandable internal spring clip, over the bevelled land of the connector body. The spring clip is finally captured in a groove around the connector body. Alternatively, internal to the coupling nut is a bevelled land which compressed a spring clip captured in a groove around the connector body as the coupling nut is pushed over the connector body. Finally the boss or the bevelled land is captured between the spring clip and the stationary clip of the connector body. However, the approaches of U.S. Pat. No. 4,711,517 require modifications of existing connector designs which are impractical in many cases. The apparatus and method described herein results in an improved approach to post-installation of the coupling nut compatible with existing connector designs.
In view of the foregoing problems, it is apparent that there is a need in the fiber optic art and industry for an improved apparatus and method for installing fiber optic cables which would allow for the tedious and time-consuming connectorization of fiber optic cables in the factory prior to the field installation of the cable. Moreover, there is a need for an approach to factory installation which can be applied to the majority of connectors being used in local area networks.
Accordingly, I have invented a new and improved method and apparatus which primarily comprises novel connector assemblies which may be assembled on the fiber optic cable in the factory where all of the tedious steps to prepare the cable and connector may be done.
It is, therefore, an object of the present invention to provide a means of reducing both the cost and complexity of fiber optic cable duct installation by enabling factory performance of the complex fiber/connector mate and polish process, while field personnel can use conventional cable installation equipment and processes to place the pre-connected cable in the customer's conduit.